Observe the figure above. Does it appear to ‘breathe’ in for 3 seconds, out for 3 seconds? Does it alternatingly move towards you (“loom”) and recede?
This illusion of motion in depth can be enhanced by observing with one eye only. Also it seems stronger with a little blur (which can be adjusted)..

Comment

All disks change their individual luminance in a sawtooth manner: slowly increasing black to white, then jumping to black again; this gives a looming illusion. During the other phase luminance jumps to white and then decreases slowly, give an illusion of receding into distance.

History

This illusion was developed by Frank Schäffel to stimulate accommodation without changes in focus and without actual motion. During our collaborative projects I saw it and was quite impressed, so I programmed this on-line version.